<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button id="btn">按钮</button>
    <!-- 直接就发了请求 -->
    <!-- <script src="http:127.0.0.1:5000/test"></script> -->
    
    <!-- ajax请求 -->
    <!-- 跨域无法发送请求，会被浏览器拦截 -->
    <script>
        btn.onclick=function(){
            const xhr=new XMLHttpRequest()
            xhr.open('get','http://127.0.0.1:5000/test')
            xhr.send()
        }
    </script>
</body>
</html>